Giant vesicles at the prolate-oblate transition: A macroscopic bistable system

TL;DR

This study demonstrates that giant phospholipid vesicles undergo thermally activated shape transitions between prolate and oblate forms, serving as a macroscopic bistable system modeled by a Kramers process.

Contribution

The paper provides experimental evidence and a theoretical framework for understanding shape bistability in giant vesicles through a Kramers model.

Findings

Transition activation energy is about k_BT.

Bimodal probability distribution of ellipticity.

Dynamics consistent with overdamped diffusion in a bistable potential.

Abstract

Giant phospholipid vesicles are shown to exhibit thermally activated transitions between a prolate and an oblate shape on a time scale of several seconds. From the fluctuating contour of such a vesicle we extract ellipticity as an effective reaction coordinate whose temporal probability distribution is bimodal. We then reconstruct the effective potential from which we derive an activation energy of the order of $k_BT$ in agreement with theoretical calculations. The dynamics of this transition is well described within a Kramers model of overdamped diffusion in a bistable potential. Thus, this system can serve as a model for macroscopic bistability.